In various photographic systems for forming images, whether in black or white or in color, it is often desirable to include in the photographic film unit one or more of the various photographic reagents required for development and/or to enhance image quality. This practice extends both to conventional systems for forming negative images and also to various systems such as diffusion transfer wherein a positive image in silver or in color is obtained.
In many instances, the photographic reagent may be contained initially in either the processing composition applied for development and image formation or in the film unit itself. The latter is typically preferred so as to reduce the number of ingredients required in the processing composition.
In other instances, the particular photographic reagent desired is not sufficiently stable in alkali to provide the requisite shelf life for the processing composition or the reagent is incompatible and/or reacts with another reagent in the processing composition and therefore must be contained initially in the film unit.
In still other instances, the reagent must be provided at some particular time in the development process which requires that it be present in a specified layer or in specified proximity to another layer in the film unit.
In all of the foregoing instances, it is desirable that the reagent be contained in the desired layer(s) of the film unit in a form which is stable and non-migratory or non-diffusible and yet available when it is required at a particular time in the development process. To accomplish this result, it is known in the art to attach to the particular photographic reagent a blocking moiety which prevents the photographic reagent from reacting with other photographic materials present in the film unit or migrating or diffusing prior to the time when photographic development is effected but which will release the photographic reagent at the desired time such as by reaction with the aqueous alkaline processing composition.
The present application relates to novel compounds which release a thio- or selenourea moiety or derivatives thereof upon contact with aqueous alkaline compositions and which are useful in photographic applications.